If I use a pre-built external HD, can I still use the same data recovery tools?

[The Red]

I just read something a little disturbing posted by another [H] user that states that if an external HD fails that its impossible to use the same recovery tools as for internal HDs after a failure? ... I got all my music, video, written works and software backups on a large pre-built external HD... Maxtor OneTouch III to be specific. If it fails, would I be able to use the same tools I used before to recover my data or is it true, its perma-dead ? ... I dont know how the pre-built ones work, but I read something about the warranty being void if I open it to connect like an internal? ... would I have to do that to recover the data? ... i've never tried running recovery tools on a usb connected external before.

My HD is not dead, this is just a pre-cautionary post. I want to know if I should keep backups on internals?